This patent application claims priority from a Japanese patent application No. 2001-096414 filed on Mar. 29, 2001, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a power supply unit. More particularly, the present invention relates to a power supply unit with a series regulator (dropper type power supply).
2. Description of the Related Art
A series regulator (dropper type power supply) is known as a power supply unit that changes an input direct current (DC) voltage input from a DC power supply into a stabilized output DC voltage.
This series regulator changes the input DC voltage to the stabilized output DC voltage that is lower than the input DC voltage.
This series regulator, however, converts a power loss generated by voltage drop between an input and an output of a semiconductor device such as a transistor, used as a three-terminal regulator device serving as a main controlling device, into heat. Thus, in a case where the voltage drop is large, the power loss in the semiconductor device also becomes large, thereby reducing the reliability of the entire product.
Therefore, it is an object of the present invention to provide a power supply unit, which is capable of overcoming the above drawbacks accompanying the conventional art. The above and other objects can be achieved by combinations described in the independent claims. The dependent claims define further advantageous and exemplary combinations of the present invention.
According to the first aspect of the present invention, a power supply unit having a series regulator that changes an input DC voltage input from a DC power supply into a stabilized output DC voltage lower than the input DC voltage, comprises: a power consuming unit, provided on a direct current path between the DC power supply and an input side of the series regulator, including a parallel circuit formed by a first fixed resistor and a semiconductor device having a current input, a current output and a setting input; and a current setting unit operable to set an amount of a current flowing between the current input and the current output of the semiconductor device, wherein the current input of semiconductor device is arranged on a DC-power-supply side thereof, the current output of the semiconductor device is arranged on a series-regulator side thereof, and the setting input of the semiconductor device is connected to a setting output of the current setting unit.
According to the second aspect of the present invention, a power supply unit having a series regulator that changes an input DC voltage input from a DC power supply into a stabilized output DC voltage lower than the input DC voltage, comprises: a first power consuming unit, provided in parallel to the series regulator, including a parallel circuit formed by a first fixed resistor and a first semiconductor device having a current input, a current output and a setting input; and a first current setting unit operable to set an amount of a current flowing between the current input and the current output of the first semiconductor device, wherein the current input of the first semiconductor device is arranged on a series-regulator-input side thereof, the current output of the first semiconductor device is arranged on a series-regulator-output side thereof, and the setting input of the first semiconductor device is connected to a setting output of the first current setting unit.
The power supply unit may further comprise: a second power consuming unit, provided on a direct current path between the DC power supply and the input of the series regulator, having a parallel circuit formed by a second fixed resistor and a second semiconductor device; and a second current setting unit operable to set an amount of a current flowing between a current input and a current output of the second semiconductor device, wherein the current input of the second semiconductor device is arranged on a DC-power-supply side thereof, the current output of the second semiconductor device is arranged on a series-regulator side thereof, and a setting input of the second semiconductor device is connected to a setting output of the second current setting unit.
In the power supply unit according to the first or second aspect of the present invention, the power consuming unit or the first or second power consuming unit may include the third fixed resistor connected to the semiconductor device in series in the parallel circuit.
In the power supply unit according to the first or second aspect of the present invention, the power consuming unit or the first or second power consuming unit may include the fourth fixed resistor connected to the parallel circuit in series.
In the power supply unit according to the first or second aspect of the present invention, the power consuming unit or the first or second power consuming unit may include a plurality of parallel circuits connected in series. Alternatively, the power consuming unit or the first or second power consuming unit may include a plurality of parallel circuits connected in parallel.
The current setting unit in the power supply unit of the first aspect of the present invention may set the amount of the current flowing through the semiconductor device by regulating a bias of the setting input of the semiconductor device. In this case, the current setting unit may include a changing unit operable to change the bias. Also, in this case, the current setting unit may regulate the bias by using a divided voltage generated by a plurality of resistor devices connected in series between the input DC voltage input from the DC power supply and a predetermined reference voltage.
Moreover, in this case, the current setting unit may use a voltage that regulates the output DC voltage of the series regulator as the predetermined reference voltage. Furthermore, the current setting unit may include a Zener diode that regulates the bias in this case.
The current setting unit may include a feedback circuit connected to the current output of the semiconductor device and an amplifying circuit having an input connected to the feedback circuit, another input to which the predetermined reference voltage is applied and an output connected to the setting input of the semiconductor device.
It is preferable that the current setting unit set the amount of the current flowing through the semiconductor device to make the amount of heat generated in the semiconductor device during an actual operation approximately equal to the amount of heat generated in the series regulator.
The first or second current setting unit in the power supply unit of the second aspect of the present invention may set the amount of the current flowing through the corresponding semiconductor device by regulating a bias of the setting input of the corresponding semiconductor device. In this case, the first or second current setting unit may include a changing unit operable to change the bias. Also, in this case, the first or second current setting unit may regulate the bias by using a divided voltage generated by a plurality of resistor devices connected in series between the input DC voltage input from the DC power supply and a predetermined reference voltage.
Moreover, in this case, the first or second current setting unit may use a voltage that regulates the output DC voltage of the series regulator as the predetermined reference voltage. Furthermore, the first or second current setting unit may include a Zener diode that regulates the bias in this case.
The first or second current setting unit may include a feedback circuit connected to the current output of the corresponding semiconductor device and an amplifying circuit having an input connected to the feedback circuit, another input to which the predetermined reference voltage is applied and an output connected to the setting input of the corresponding semiconductor device.
It is preferable that the first or second current setting unit set the amount of current flowing through the corresponding semiconductor device to make the amount of heat generated by the corresponding semiconductor device during an actual operation approximately equal to the amount of heat generated by the series regulator.
In the power supply unit according to the first aspect of the present invention, the series regulator may have a Zener diode that regulates the output DC voltage of the series regulator, the power consuming unit has the parallel circuit formed by the first fixed resistor and an npn transistor as the semiconductor device that are connected in parallel, a collector, an emitter and a base of the npn transistor serving as the current input, the current output and the setting input of the semiconductor device, respectively; the current setting unit may include a resistor series circuit formed by a plurality of resistor devices connected in series, one end of the resistor series circuit being connected to the DC power supply, the other end being connected to a cathode terminal of the Zener diode; and a divided voltage generated at the setting output of the current setting unit, that is positioned between the plurality of resistor devices, may be applied to the base of the npn transistor.
In this case, the current setting unit may include the third fixed resistor in the parallel circuit so as to be provided between the collector of the npn transistor and the input end of the series regulator.
Moreover, in this case, the power supply unit according to the first aspect of the present invention may include the fourth fixed resistor in the parallel circuit to be provided between the emitter-end of the parallel circuit and the input end of the series regulator. In addition, the fourth fixed resistor may be provided between the collector-end of the parallel circuit and the DC power supply.
In the power supply unit according to the first aspect of the present invention, the series regulator may have a Zener diode that regulates the output DC voltage of the series regulator; the power consuming unit may have the parallel circuit formed by the first fixed resistor and a pnp transistor as the semiconductor device that are connected in parallel, an emitter, a collector and a base of the pnp transistor serving as the current input, the current output and the setting input of the semiconductor device, respectively; and the current setting unit may include a resistor series circuit formed by a plurality of resistor devices connected in series and an npn transistor, one end of the resistor series circuit being connected to the DC power supply, the other end being connected to a cathode terminal of the Zener diode. In the npn transistor, a divided voltage generated at the setting output of the current setting unit, that is positioned between the plurality of resistor devices, is applied to the base; an emitter is connected to the series regulator; and a collector is connected to the DC power supply via the first one of the plurality of resistor devices and to the base of the pnp transistor via the second one of the plurality of resistor devices.
In this case, the fourth fixed resistor may be provided in the parallel circuit between the collector-end of the parallel circuit and the input end of the series regulator.
In the power supply unit according to the first aspect of the present invention, the series regulator may include the first Zener diode operable to regulate the output DC voltage of the series regulator and the first Zener resistor connected between a cathode terminal of the first Zener diode and the input of the series regulator; the power consuming unit includes the parallel circuit formed by an npn transistor as the semiconductor device and the first fixed resistor that are connected in parallel, a collector, an emitter and a base of the npn transistor respectively serving as the current input, the current output and the setting input of the semiconductor device; the current setting unit may include the second Zener diode and the second Zener resistor connected between a cathode terminal of the second Zener diode and the DC power supply; and the setting output of the current setting unit may be the cathode terminal of the second Zener diode, a Zener voltage generated at the cathode terminal of the second Zener diode being applied to the base of the npn transistor in the parallel circuit.
In the power supply unit according to the first aspect of the present invention, the series regulator may include a Zener diode operable to regulate the output DC voltage of the series regulator; the power consuming unit may include a plurality of parallel circuits connected in series each of which is formed by an npn transistor as the semiconductor device and the first fixed resistor connected in parallel, a collector, an emitter and a base of the npn transistor respectively serving as the current input, the current output and the setting input of the semiconductor device; the current setting unit may include a resistor series circuit formed by a plurality of resistor devices connected in series, one end of the resistor series circuit being connected to the DC power supply while the other end is connected to a cathode terminal of the Zener diode, the number of the resistor devices corresponding to the number of the parallel circuits in the power consuming circuit; the setting output of the current setting unit may be respective connection points between the plurality of resistor devices; and divided voltages, different from each other, generated at the respective connection points may be applied to the bases of the npn transistors in the respective parallel circuits in accordance with an order in which the npn transistors are arranged.
Moreover, in the power supply unit according to the first aspect of the present invention, the series regulator may include a Zener diode operable to regulate the output DC voltage of the series regulator; the power consuming unit may include a plurality of parallel circuits connected in series each of which is formed by an npn transistor as the semiconductor device and the first fixed resistor connected in parallel, a collector, an emitter and a base of the npn transistor respectively serving as the current input, the current output and the setting input of the semiconductor device; the current setting unit may include a resistor series circuit formed by a plurality of resistor devices connected in series, one end of the resistor series circuit being connected to the DC power supply while the other end is connected to a cathode terminal of the Zener diode, the number of the resistor devices being equal to the number of the parallel circuits in the power consuming circuit; the setting output of the current setting unit may be respective connection points between the plurality of resistor devices; and divided voltages generated at the respective connection points may be applied to the bases of the npn transistors in the respective parallel circuits.
In the power supply unit according to the first aspect of the present invention, the power consuming unit may include the parallel circuit formed by an npn transistor as the semiconductor device and the first fixed resistor connected in parallel, a collector, an emitter and a base of the npn transistor respectively serving as the current input, the current output and the setting input of the semiconductor device; the current setting unit may include a feedback circuit connected to the emitter of the npn transistor and an inverting amplifying circuit having an inverting input connected to the feedback circuit and a non-inverting input to which the predetermined reference voltage for regulating the output DC voltage of the series regulator is applied; and the setting output of the current setting unit may be an output of the inverting amplifying circuit that is connected to the base of the npn transistor.
In the power supply unit according to the first aspect of the present invention, the power consuming unit may include the parallel circuit formed by a pnp transistor as the semiconductor device and the first fixed resistor connected in parallel, an emitter, a collector and a base of the pnp transistor respectively serving as the current input, the current output and the setting input of the semiconductor device; the current setting unit may include a feedback circuit connected to the collector of the pnp transistor, an inverting amplifying circuit where an inverting input is connected to the feedback circuit, to a non-inverting input is applied the predetermined reference voltage for regulating the output DC voltage of the series regulator, and an output is connected to the base of the pnp transistor, and an npn transistor having a base connected to the output of the inverting amplifying circuit and an emitter connected to the predetermined reference voltage; and the setting output of the current setting unit may be a collector of the npn transistor, that is connected to the base of the pnp transistor.
According to the third aspect of the present invention, a power supply unit having a series regulator that changes an input DC voltage input from a DC power supply into a stabilized output DC voltage lower than the input DC voltage, comprises: the fifth fixed resistor connected to the series regulator in parallel; and a clamp diode operable to clamp an output voltage to be a predetermined voltage between the input DC voltage and the output DC voltage.
The clamp diode may be a Zener diode having a cathode terminal connected to the output of the series regulator and an anode terminal connected to a reference voltage of the series regulator.
In the power supply unit according to the third aspect of the present invention, the series regulator may include a Zener diode operable to regulate the output DC voltage of the series regulator and a Zener resistor connected between a cathode terminal of the Zener diode and the input of the series regulator; and the clamp diode may be formed by a diode having an anode terminal connected to the output of the series regulator and a cathode terminal connected to the cathode terminal of the Zener diode, and another Zener diode.
In the power supply unit according to the third aspect of the present invention, the series regulator may include a Zener diode operable to regulate the output DC voltage of the series regulator; the power supply unit may further comprise a power consuming unit including a parallel circuit formed by an npn transistor and the first fixed resistor connected in parallel, and a current setting unit including a resistor series circuit formed by a plurality of resistor devices connected in series, one end of the resistor series circuit being connected to the DC power supply while the other end is connected to a cathode terminal of the Zener diode, a divided voltage generated at a setting output of the current setting unit, that is located between the plurality of resistor devices, being applied to a base of the npn transistor so as to regulate the amount of a current flowing between a collector and an emitter of the npn transistor which respectively serve as a current input and a current output thereof; and the clamp diode may be formed by a diode having an anode terminal connected to the output of the series regulator and a cathode terminal connected to the cathode terminal of the Zener diode, and another Zener diode.
In any of the power supply units according to the first, second and third aspects of the present invention, it is desirable that the respective fixed resistor be formed by printing on a printed board, for example, of aluminum or ceramic.
The summary of the invention does not necessarily describe all necessary features of the present invention. The present invention may also be a sub-combination of the features described above. The above and other features and advantages of the present invention will become more apparent from the following description of the embodiments taken in conjunction with the accompanying drawings.